Understand that they don't mean exactly the same thing. 'I like improving' means that I find pleasure in whatever improvement I've made (as I continue to practice) or that I might make in the future. 'I would like to improve' means that my goal (my objective, my desire) is to improve. Similarly, 'I like practicing' means that I find the process of practicing enjoyable, whereas 'I'd like to practice' means that I want want to practice.

"Would like" always take "to-infinitives". You can say "I'd like to improve" or "I'd like to practice". You can also say "I like improving" or "I like practicing". Of course, "I'd like to" and "I like" means two different things. "I'd like to X" means "I haven't done X yet but I want to do X" while "I like Y" means "I already do Y and I enjoy doing Y". Hope this helped!